Finder optical system

Abstract

The invention provides a real-image type finder optical system which is reduced in size in general and thickness in particular. In order from an object side of the system, the system comprises an objective optical subsystem having a positive refracting power, an image-inversion component for erecting a real image formed by the objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface. The objective optical subsystem comprises at least two reflecting surfaces of reflecting surfaces 12 to 14, each defined by a rotationally asymmetric surface with power imparted thereto. At least one reflecting surface 13 of the reflecting surfaces is defined by a reflecting surface that is not the same surface as a transmitting surface, and satisfies 5°<|theta|<25° where theta is the angle of reflection of an axial chief ray with the normal to the reflecting surface 13 that is not the same surface as a transmitting surface.

What we claim is:  
     
       1. A finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image, and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises at least two reflecting surfaces, each defined by a rotationally asymmetric surface having a power, and at least one of said reflecting surfaces is defined by a reflecting surface that is not the same surface as a transmitting surface, with said at least one reflecting surface satisfying the following condition (1):  
       
         
           5°<|θ|<25°  (1)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to said reflecting surface that is not the same surface as the transmitting surface.  
     
     
       2. A finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image formation action to an erect image, and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises at least a plurality of reflecting surfaces, each defined by a rotationally asymmetric surface having a power, and at least two of said reflecting surfaces are each defined by a reflecting surface that is not the same surface as a transmitting surface, with at least one of said at least two reflecting surfaces satisfying the following condition (1):  
       
         
           5°<|θ|<45°  (3)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to said reflecting surface that is not the same surface as the transmitting surface.  
     
     
       3. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image- inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, each of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface and a first reflecting surface satisfying the following condition (5):  
       
         
           5°<|θ|<25°  (5)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the first reflecting surface.  
     
     
       4. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least two reflecting surfaces of which are each defined by a rotationally asymmetric surface, with a first reflecting surface being defined by the same surface as a second transmitting surface and a third reflecting surface being defined by the same surface as a first transmitting surface, and the second reflecting surface of said reflecting surfaces of said prism has a strongest power.  
     
     
       5. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least two reflecting surfaces of which are each defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same as a second transmitting surface or both a first transmitting surface and a second transmitting surface.  
     
     
       6. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising four reflecting surfaces, at least two reflecting surfaces of which are each defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface and a third reflecting surface being defined by the same surface as a second transmitting surface.  
     
     
       7. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising reflecting surfaces, each of which is defined by a rotationally asymmetric surface, with first and second reflecting surfaces being independent of first and second transmitting surfaces, and having a power of the same sign.  
     
     
       8. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least two reflecting surfaces of which are each defined by a rotationally asymmetric surface, with all first to third reflecting surfaces being defined by surfaces independent of first and second transmitting surfaces.  
     
     
       9. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface and a first reflecting surface satisfying the following condition (7), and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a first reflecting surface being defined by the same surface as a second transmitting surface and a third reflecting surface being defined by the same surface as a first transmitting surface:  
       
         
           5°<|θ|<25°  (7)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the first reflecting surface of said prism in said objective optical subsystem.  
     
     
       10. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a first reflecting surface being defined by the same surface as a second transmitting surface and a third reflecting surface being defined by the same surface as a first transmitting surface, while the following condition (9) is satisfied:  
       
         
           0.1 <d/Ih< 2.5  (9)  
         
       
       where d is a distance along an axial chief ray from the first transmitting surface to an entrance pupil of said prism in said objective optical subsystem, and Ih is a maximum intermediate image-formation height.  
     
     
       11. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, in which an axial chief ray does not cross over itself, and all first, second and third reflecting surfaces are defined by surfaces independent of first and second transmitting surfaces.  
     
     
       12. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a first reflecting surface being defined by the same surface as a second transmitting surface, and all first, and a third reflecting surface being defined by a surface independent of first and second transmitting surfaces.  
     
     
       13. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a second reflecting surface being defined by the same surface as a second transmitting surface.  
     
     
       14. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a second reflecting surface being defined by the same surface as a first transmitting surface.  
     
     
       15. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a third reflecting surface being defined by the same surface as a first transmitting surface, and all first, and a first reflecting surface being defined by a surface independent of first and second transmitting surfaces.  
     
     
       16. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a first reflecting surface being defined by the same surface as a second transmitting surface and a second reflecting surface being defined by the same surface as the first transmitting surface.  
     
     
       17. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, with a second reflecting surface being defined by the same surface as a second transmitting surface, and a third reflecting surface being defined by the same surface as a first transmitting surface.  
     
     
       18. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a first reflecting surface being defined by the same surface as a second transmitting surface and a third reflecting surface being defined by the same surface as a first transmitting surface, said second reflecting surface having a strongest power, and said ocular optical subsystem comprises a prism comprising two reflecting surfaces, with a second transmitting surface being defined by the same surface as a first reflecting surface.  
     
     
       19. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a first reflecting surface being defined by the same surface as a second transmitting surface and a third reflecting surface being defined by the same surface as a first transmitting surface, and said ocular optical subsystem comprises a prism which comprises four reflecting surfaces, and in which an axial chief ray does not cross over itself.  
     
     
       20. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as both a first transmitting surface and a second transmitting surface, and said ocular optical subsystem comprises a prism comprising two reflecting surfaces, which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface.  
     
     
       21. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising four reflecting surfaces, at least two reflecting surfaces of which are each defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface and a third reflecting surface being defined by the same surface as a second transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface, with an axial chief ray crossing over itself between a first reflecting surface and a second reflecting surface.  
     
     
       22. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising four reflecting surfaces, at least two reflecting surfaces of which are each defined by a rotationally asymmetric surface, with a second reflecting surface being defined by the same surface as a first transmitting surface and a third reflecting surface being defined by the same surface as a second transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces, which are all defined by surfaces independent of said first transmitting surface and said second transmitting surface, with an axial chief ray crossing over itself between a second reflecting surface and a third reflecting surface.  
     
     
       23. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, and which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface and have a power of the same sign, and said ocular optical subsystem comprises a prism comprising one reflecting surface.  
     
     
       24. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface, and either one of which satisfies the following condition (11), and said ocular optical subsystem comprises a prism comprising one reflecting surface:  
       
         
           5°<|θ|<45°  (11)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the first reflecting surface or the second reflecting surface.  
     
     
       25. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, and which are all defined by surfaces independent of a first transmitting surf ace and a second transmitting surface, and said ocular optical subsystem comprises a prism comprising one reflecting surface, while the following condition (13) is satisfied:  
       
         
           0.1 <d/Ih< 2.5  (13)  
         
       
       where d is a distance along an axial chief ray from the first transmitting surface to an entrance pupil of said prism in said objective optical subsystem, and Ih is a maximum intermediate image-formation height.  
     
     
       26. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, and which are defined by surfaces independent of a first transmitting surface and a second transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface, with an axial chief ray being reflected from a first reflecting surface to an object side.  
     
     
       27. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising two reflecting surfaces, at least one reflecting surface of which is defined by a rotationally asymmetric surface, and which are defined by surfaces independent of a first transmitting surface and a second transmitting surface, and said ocular optical subsystem comprises a prism comprising three reflecting surfaces which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface, with an axial chief ray being reflected from a first reflecting surface to a pupil side.  
     
     
       28. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least two reflecting surfaces of which is each defined by a rotationally asymmetric surface, and which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface, and said ocular optical subsystem comprises a prism comprising two reflecting surfaces, with a second transmitting surface being defined by the same surface as a first reflecting surface.  
     
     
       29. A real-image type finder optical system comprising, in order from an object side thereof, an objective optical subsystem having a positive refracting power, an image-inversion means for erecting a real image formed by said objective optical subsystem having only one image-formation action to an erect image and an ocular optical subsystem having a positive refracting power, with at least one of reflecting surfaces being defined by a roof surface, wherein: 
       said objective optical subsystem comprises a prism comprising three reflecting surfaces, at least two reflecting surfaces of which is each defined by a rotationally asymmetric surface, and which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface, and said ocular optical subsystem comprises a prism comprising two reflecting surfaces which are all defined by surfaces independent of a first transmitting surface and a second transmitting surface.  
     
     
       30. The real-image type finder optical system according to claim  1 , wherein said objective optical subsystem, and said ocular optical subsystem comprise at least one prism that is said image-inversion means. 
     
     
       31. The real-image type finder optical system according to claim  1 , wherein said objective optical subsystem comprises one positive-power prism including said image-inversion means. 
     
     
       32. The real-image type finder optical system according to claim  1 , wherein said ocular optical subsystem comprises at least one refracting lens free from any reflecting surface. 
     
     
       33. The real-image type finder optical system according to claim  1 , wherein said roof surface is used for a reflecting surface included in said image-inversion means located on an pupil side with respect to an intermediate image-formation plane. 
     
     
       34. The real-image type finder optical system according to claim  7 , wherein said image-inversion means located on a pupil side with respect to an intermediate image-formation plane comprises one reflecting surface. 
     
     
       35. The real-image type finder optical system according to any one of claims  4 ,  5  and  8 , wherein said image-inversion means located on a pupil side with respect to an intermediate image-formation plane comprises two reflecting surfaces. 
     
     
       36. The real-image type finder optical system according to any one of claims  3 ,  6  and  7 , wherein said image-inversion means located on a pupil side with respect to an intermediate image-formation plane comprises three reflecting surfaces. 
     
     
       37. The real-image type finder optical system according to claim  4 , wherein said image-inversion means located on a pupil side with respect to an intermediate image-formation plane comprises four reflecting surfaces. 
     
     
       38. The real-image type finder optical system according to claim  4 , wherein the reflecting surface that is not the same surface as a transmitting surface in said objective optical subsystem satisfies the following condition (15): 
       
         
           5°<|θ|<25°  (15)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the reflecting surface that is not the same as a transmitting surface.  
     
     
       39. The real-image type finder optical system according to claim  3 , wherein the reflecting surface that is not the same surface as a transmitting surface in said objective optical subsystem satisfies the following condition (16): 
       
         
           5°<|θ|<21.5°  (16)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the reflecting surface that is not the same as a transmitting surface.  
     
     
       40. The real-image type finder optical system according to claim  5 , wherein any one of the reflecting surfaces that are not the same surface as transmitting surfaces in said objective optical subsystem satisfies the following condition (17): 
       
         
           5°<|θ|<45°  (17)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the reflecting surfaces that are not the same as transmitting surfaces.  
     
     
       41. The real-image type finder optical system according to claim  5 , wherein any one of the reflecting surfaces that are not the same surface as transmitting surfaces in said objective optical subsystem satisfies the following condition (18): 
       
         
           5°<|θ|<37°  (18)  
         
       
       where θ is an angle of reflection of an axial chief ray with respect to a normal to the reflecting surfaces that are not the same as transmitting surfaces.  
     
     
       42. The real-image type finder optical system according to claim  1 , wherein an entrance pupil position of said objective optical subsystem satisfies the following condition (19): 
       
         
           0.1 <d/Ih< 2.5  (19)  
         
       
       where d is a distance along an axial chief ray of a first transmitting surface to an entrance pupil of a prism located in said objective optical subsystem.  
     
     
       43. The real-image type finder optical system according to claim  1 , wherein an entrance pupil position of said objective optical subsystem satisfies the following condition (20): 
       
         
           0.2 <d/Ih< 1.2  (20)  
         
       
       where d is a distance along an axial chief ray of a first transmitting surface to an entrance pupil of a prism located in said objective optical subsystem.  
     
     
       44. The finder optical system according to claim  1 , wherein a ray passing through an center of an entrance pupil of said objective optical subsystem satisfies the following condition (21): 
       
         
           −5°<α<15°  (21)  
         
       
       where α is a maximum exit angle of said objective optical subsystem on the base of an axial chief ray.  
     
     
       45. The finder optical system according to claim  1 , wherein a ray passing through an center of an entrance pupil of said objective optical subsystem satisfies the following condition (22): 
       
         
           −1°<α<7°  (22)  
         
       
       where α is a maximum exit angle of said objective optical subsystem on the base of an axial chief ray.  
     
     
       46. The finder optical system according to claim  5 , wherein an angle between a ray incident on said objective optical subsystem and a ray incident on an intermediate image-formation plane satisfies the following condition (23): 
       
         
           0°≦|φ|<30°  (23)  
         
       
       where φ is an angle between a center chief ray incident on said objective optical subsystem and a center chief ray incident on an intermediate image-formation plane.  
     
     
       47. The finder optical system according to claim  5 , wherein an angle between a ray incident on said objective optical subsystem and a ray incident on an intermediate image-formation plane satisfies the following condition (24): 
       
         
           0°≦|φ|<20 °  (24)  
         
       
       where φ is an angle between a center chief ray incident on said objective optical subsystem and a center chief ray incident on an intermediate image-formation plane.  
     
     
       48. The finder optical system according to claim  3 , wherein an angle between a ray incident on said objective optical subsystem and a ray incident on an intermediate image-formation plane satisfies the following condition (25): 
       
         
           30°<|φ|<80°  (25)  
         
       
       where φ is an angle between a center chief ray incident on said objective optical subsystem and a center chief ray incident on an intermediate image-formation plane.  
     
     
       49. The finder optical system according to claim  3 , wherein an angle between a ray incident on said objective optical subsystem and a ray incident on an intermediate image-formation plane satisfies the following condition (26): 
       
         
           40°<|φ|<70°  (26)  
         
       
       where φ is an angle between a center chief ray incident on said objective optical subsystem and a center chief ray incident on an intermediate image-formation plane.  
     
     
       50. The finder optical system according to claim  7 , wherein an angle between a ray incident on said objective optical subsystem and a ray incident on an intermediate image-formation plane satisfies the following condition (27): 
       
         
           60°<|φ|≦90°  (27)  
         
       
       where φ is an angle between a center chief ray incident on said objective optical subsystem and a center chief ray incident on an intermediate image-formation plane.  
     
     
       51. The finder optical system according to claim  7 , wherein an angle between a ray incident on said objective optical subsystem and a ray incident on an intermediate image-formation plane satisfies the following condition (28): 
        70°<|φ|≦90°  (15) 
       where φ is an angle between a center chief ray incident on said objective optical subsystem and a center chief ray incident on an intermediate image-formation plane.  
     
     
       52. The finder optical system according to claim  1 , which has a finder magnification satisfying the following condition (29): 
       
         
           0.05 <m< 10  (29)  
         
       
       where m is a finder magnification defined by a focal length of said objective optical subsystem divided by a focal length of said ocular optical subsystem.  
     
     
       53. The finder optical system according to claim  1 , which has a finder magnification satisfying the following condition (30): 
       
         
           0.1 <m< 2     (30)  
         
       
       where m is a finder magnification defined by a focal length of said objective optical subsystem divided by a focal length of said ocular optical subsystem.  
     
     
       54. The finder optical system according to claim  1 , wherein said objective optical subsystem has an entrance half angle of view satisfying the following condition (31): 
       
         
           1°<α ob <45°  (31)  
         
       
       where α ob  is a maximum entrance half angle of view of said objective optical subsystem.  
     
     
       55. The finder optical system according to claim  1 , wherein said objective optical subsystem has an entrance half angle of view satisfying the following condition (32): 
       
         
           5°<α ob <45°  (32)  
         
       
       where α ob  is a maximum entrance half angle of view of said objective optical subsystem.  
     
     
       56. The finder optical system according to claim  1 , wherein said ocular optical subsystem has an exit angle satisfying the following condition (33): 
       
         
           1°α ob <30°  (33)  
         
       
       where α oc  is a maximum exit angle of said ocular optical subsystem.  
     
     
       57. The finder optical system according to claim  1 , wherein said ocular optical subsystem has an entrance half angle of view satisfying the following condition (34): 
       
         
           3°<α oc <20°  (34)  
         
       
       where α oc  is a maximum exit angle of said ocular optical subsystem.  
     
     
       58. The finder optical system according to claim  1 , wherein said rotationally asymmetric surface is a free-form surface having only one plane of symmetry.